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Boardworks GCSE Additional Science: Chemistry Rates of Reaction

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Presentation on theme: "Boardworks GCSE Additional Science: Chemistry Rates of Reaction"— Presentation transcript:

1 Boardworks GCSE Additional Science: Chemistry Rates of Reaction
Kinetics

2 Boardworks GCSE Additional Science: Chemistry Rates of Reaction

3 What does rate of reaction mean?
Boardworks GCSE Additional Science: Chemistry Rates of Reaction The speed of different chemical reactions varies hugely. Some reactions are very fast and others are very slow. The speed of a reaction is called the rate of the reaction. What is the rate of these reactions? Airbag Reaction rusting baking explosion Photo credit: © 2007 Jupiterimages Corporation slow fast very fast

4 Boardworks GCSE Additional Science: Chemistry Rates of Reaction
Why are some reactions faster than others? Teacher notes This illustration contains several discussion points relating to rates of reaction, including: Red characters: these represent particles that have a large amount of kinetic energy and are therefore likely to react. Blue characters : these represent particles that have a small amount of kinetic energy and are therefore unlikely to react (hence why some are asleep). Bumper cars: the collision between two bumper cars represents the large amount of energy released during a reaction.

5 Measuring the rate of a reaction
Boardworks GCSE Additional Science: Chemistry Rates of Reaction The change in concentration can be measured by using any property that changes during the reaction. These may include Mass or volume changes for gaseous reactions. Change in pH for reactions involving acids and bases. Changes in conductivity measurements for reactions involving electrolytes. Teacher notes See the ‘Energy Transfer’ presentation for more information on activation energy. Use of a spectrometer or colorimeter for reactions involving change in colour.

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Collision Theory Boardworks GCSE Additional Science: Chemistry Rates of Reaction For a reaction to take place between two reactant particles, three conditions are necessary: The two particles must collide with each other. They must collide in the correct orientation, so that the reactive parts of each particle will come into contact with each other. The reactants must collide with sufficient kinetic energy to bring about the raction. Teacher notes See the ‘Energy Transfer’ presentation for more information on activation energy.

7 Graphing rates of reaction
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This animated graph summarizes the qualitative information provided by the gradient of a graph that plots amount of product in a reaction against time.

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Reactant–product mix Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This animated graph follows-on from the graph on the previous slide, and illustrates how the change in the rate of a reaction can be explained in terms of changing amounts of reactants and product.

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Activation Energy Boardworks GCSE Additional Science: Chemistry Rates of Reaction The minimum amount of energy required to bring out the reaction is called the Activation Energy Teacher notes See the ‘Energy Transfer’ presentation for more information on activation energy. The activation energy (Ea) for the forward reaction is shown by (a) The activation energy (Ea) for the reverse reaction is shown by (b)

10 Setting up rate experiments
Boardworks GCSE Additional Science: Chemistry Rates of Reaction What equipment is needed to investigate the rate of hydrogen production? gas syringe rubber bung rubber connecter glass tube conical flask magnesium hydrochloric acid

11 Calculating rate of reaction from graphs
Boardworks GCSE Additional Science: Chemistry Rates of Reaction How can the rate of reaction be calculated from a graph? 70 60 50 x rate of reaction = x y 40 hydrogen produced (cm3) 30 y 20 10 10 20 30 40 50 time (seconds) The gradient of the graph is equal to the initial rate of reaction at that time rate of reaction = 20 s 45 cm3 rate of reaction = 2.25 cm3/s

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Slower and slower! Boardworks GCSE Additional Science: Chemistry Rates of Reaction Reactions do not proceed at a steady rate. They start off at a certain speed, then get slower and slower until they stop. As the reaction progresses, the concentration of reactants decreases. This reduces the frequency of collisions between particles and so the reaction slows down. 0% 25% 50% 75% 100% percentage completion of reaction reactants product

13 The reactant/product mix
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This drag and drop activity provides the opportunity for informal assessment of students’ understanding of how the rate of reaction varies with the relative amounts of reactants and product.

14 Changing the rate of reactions
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Anything that increases the number of successful collisions between reactant particles will speed up a reaction. What factors affect the rate of reactions? increased temperature increased concentration of dissolved reactants, and increased pressure of gaseous reactants increased surface area of solid reactants.(decrease particle size) use of a suitable catalyst.

15 Collisions and reactions: summary
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This completing sentences activity could be used as a plenary or revision exercise on rates of reaction. Students could be asked to write down the missing words in their books and the activity could be concluded by the completion on the IWB.

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17 Temperature and collisions
Boardworks GCSE Additional Science: Chemistry Rates of Reaction How does temperature affect the rate of particle collision?

18 Effect of temperature on rate
Boardworks GCSE Additional Science: Chemistry Rates of Reaction The higher the temperature, the faster the rate of a reaction. In many reactions, a rise in temperature of 10 °C causes the rate of reaction to approximately double. Why increasing the temperature will increase the rate of reaction?

19 Temperature and particle collisions
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This simulation illustrates how increasing the temperature increases the number of collisions between particles.

20 Effect of temperature on rate
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Increasing the temperature will make the particles move faster, so there will be more collisions. At a higher temperature, many more particles will have the necessary activation energy. The ratio of successful collision to unsuccessful collisions will increase. Which one will contribute more towards increasing the rate of reaction?

21 How does temperature affect rate?
Boardworks GCSE Additional Science: Chemistry Rates of Reaction The reaction between sodium thiosulfate and hydrochloric acid produces sulfur. hydrochloric acid sodium chloride sulfur sodium thiosulfate + water sulfur dioxide Na2S2O3 (aq) 2HCl (aq) 2NaCl (aq) S (s) + SO2 (g) H2O (l) Sulfur is solid and so it turns the solution cloudy. How can this fact be used to measure the effect of temperature on rate of reaction?

22 The effect of temperature on rate
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This animation can be used to introduce the reaction between sodium thiosulfate and hydrochloric acid as a way of measuring the effect of temperature on rate of reaction. It could be shown as precursor to running the experiment in the lab, or as a revision exercise.

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24 Effect of concentration on rate of reaction
Boardworks GCSE Additional Science: Chemistry Rates of Reaction The higher the concentration of a dissolved reactant, the faster the rate of a reaction. Why does increased concentration increase the rate of reaction? At a higher concentration, there are more particles in the same amount of space. This means that the particles are more likely to collide and therefore more likely to react. The ratio of successful collisions to unsuccessful collisions will stay the same, but there will be more successful collisions. higher concentration lower concentration

25 Concentration and particle collisions
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This simulation illustrates how increasing the concentration increases the number of collisions between particles.

26 The effect of concentration on rate
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This animation can be used to introduce the reaction between magnesium and hydrochloric acid as a way of measuring the effect of concentration on rate of reaction. It could be shown as precursor to running the experiment in the lab, or as a revision exercise.

27 Effect of pressure on rate of reaction
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Why does increasing the pressure of gaseous reactants increase the rate of reaction? As the pressure increases, the space in which the gas particles are moving becomes smaller. The gas particles become closer together, increasing the frequency of collisions. This means that the particles are more likely to react. lower pressure higher pressure

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29 Effect of surface area on rate of reaction
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Any reaction involving a solid can only take place at the surface of the solid. If the solid is split into several pieces, the surface area increases. What effect will this have on rate of reaction? low surface area high surface area This means that there is an increased area for the reactant particles to collide with. The smaller the pieces, the larger the surface area. This means more collisions and a greater chance of reaction.

30 Surface area and particle collisions
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This simulation illustrates how increasing the surface area increases the number of collisions between particles and solid reactants

31 Reaction between a carbonate and acid
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Marble chips are made of calcium carbonate. They react with hydrochloric acid to produce carbon dioxide. hydrochloric acid calcium chloride calcium carbonate + water carbon dioxide CaCO3 (aq) 2HCl (aq) CaCl2 (aq) + H2O (aq) CO2 (g) The effect of increasing surface area on the rate of reaction can be measured by comparing how quickly the mass of the reactants decreases using marble chips of different sizes.

32 The effect of surface area on rate
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This animation can be used to introduce the reaction between marble chips (calcium carbonate) and hydrochloric acid as a way of measuring the effect of surface on rate of reaction. It could be shown as precursor to running the experiment in the lab, or as a revision exercise.

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What are catalysts? Boardworks GCSE Additional Science: Chemistry Rates of Reaction Catalysts are substances that change the rate of a reaction without being used up in the reaction. Catalysts never produce more product – they just produce the same amount more quickly. reaction (time) energy (kJ) Ea without catalyst Different catalysts work in different ways, but most provide an alternative path with lower activation energy (Ea). Ea with catalyst Teacher notes See the ‘Energy Transfer’ presentation for more information on activation energy.

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How do catalysts work? Boardworks GCSE Additional Science: Chemistry Rates of Reaction More of the reactants will possess this lower activation energy. Teacher notes See the ‘Energy Transfer’ presentation for more information on activation energy.

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Everyday catalysts Boardworks GCSE Additional Science: Chemistry Rates of Reaction Many catalysts are transition metals or their compounds. For example: Nickel is a catalyst in the production of margarine (hydrogenation of vegetable oils). Iron is a catalyst in the production of ammonia from nitrogen and hydrogen (the Haber process). Platinum is a catalyst in the catalytic converters of car exhausts. It catalyzes the conversion of carbon monoxide and nitrogen oxide into the less polluting carbon dioxide and nitrogen. Photo credit: © 2007 Jupiterimages Corporation Teacher notes See the ‘Reversible Reactions’ presentation for more information on the Haber process.

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37 Boardworks GCSE Additional Science: Chemistry Rates of Reaction
Glossary Boardworks GCSE Additional Science: Chemistry Rates of Reaction activation energy – The amount of energy needed to start a reaction. catalyst – A substance that increases the rate of a chemical reaction without being used up. concentration – The number of molecules of a substance in a given volume. enzyme – A biological catalyst. rate of reaction – The change in the concentration over a certain period of time.

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Anagrams Boardworks GCSE Additional Science: Chemistry Rates of Reaction

39 Rates of reaction: summary
Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This completing sentences activity provides the opportunity for some informal assessment of students’ understanding of rates of reaction.

40 Boardworks GCSE Additional Science: Chemistry Rates of Reaction
Multiple-choice quiz Boardworks GCSE Additional Science: Chemistry Rates of Reaction Teacher notes This multiple-choice quiz could be used as a plenary activity to assess students’ understanding of rates of reaction. The questions can be skipped through without answering by clicking “next”. Students could be asked to complete the questions in their books and the activity could be concluded by the completion on the IWB.


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